Patients with acutely stunned myocardium after myocardial infarction (MI) or with chronically ischemic hibernating myocardium demonstrate hypokinetic but viable left ventricular segments which improve contractile function after revascularization. Therefore, revascularization by balloon angioplasty (PTCA) or coronary artery bypass surgery (CAB) may be indicated after MI or in chronic ischemic cardiomyopathy if viable myocardium remains distal to flow limiting stenoses. In 292 patients in our thrombolysis trial for acute MI, 45% of patients improved left ventricular (LV) ejection fraction (EF) whereas the balance did not, thereby implying completed infarction without follow up revascularization being indicated. In our recent 3 year follow up of 35 post MI patients after positron emission tomography (PET), 54% of patients needed revascularization of viable myocardium at risk, consistent with previous observations that half of patients with MI have remaining viable myocardium suitable for revascularization, the question being which patients. If myocardial viability by PET were the primary basis for decisions from what was done in these patients, an alternative opposite interventional decision from what was actually done i.e., medical vs. PTCA/CAB would have been made in 37% of patients. Currently, no imaging method has been clinically validated for quantitating the size of myocardial zone at risk distal to a stenosis, the percent of this zone at risk that is viable and the percent that is necrotic as the basis for PTCA or CAB. Therefore, a definitive, controlled, randomized, prospective study of statistically appropriate sample size is proposed for patients after MI or with ischemic cardiomyopathy to predict quantitative improvement-in LV function after PTCA/CAB carried out based on quantitative sizing of myocardial necrosis, viability and zone at risk distal to all significant stenoses using a protocol combining resting rubidium washout with dipyridamole perfusion imaging. The specific aims are to document definitively in patients after acute MI or with chronic ischemic cardiomyopathy that non invasive PET with generator produced rubidium-82 provides the following (a) Quantitation of the percent of LV that is necrotic, the percent that is viable and the size of the zone at risk distal to all flow limiting stenoses including the infarct related artery. (b)In patients randomized to a PET group for which revascularization is based on PET, LV function in these revascularized patients improves substantially more than in patients randomly assigned to a standard care group where revascularization is not based on PET. (c) LV function improves in patients at one year and two years after PTCA or CAB done on the basis of remaining viability in arterial zone at risk by PET using a resting rubidium washout-dipyridamole imaging protocol. (d) LV function does not improve in patients without viable myocardium at risk distal to stenoses without PTCA or CAB due to completed infarction followed over comparable time periods. The significance of the project is both conceptual/mechanistic, addressing the causal relation of what is called "viability" to recovery of LV function, and practical/clinical, addressing a quantitative solution to a major medical problem with potentially significant improvement in selection of patients for PTCA or CAB.